Copolyetheresters are well known and have enjoyed continued and increasing commercial success. They are available from several sources including the Hytrel.RTM. resins from E.I. duPont and the GAFLEX.RTM. resins from GAF Corporation and are described in U.S. Pat. Nos. 3,023,192; 3,651,014; 3,763,109; 3,766,146; 3,784,520; 3,801,547; 4,156,774; 4,264,761 and 4,355,155, among others, all incorporated herein by reference. While these copolyetheresters have a number of desirable properties including excellent tear strength, flex life, toughness, and general elastomeric stress-strain characteristics, their use is limited by their low flexural modulus. Generally, depending upon their formulation, copolyetheresters suitable for molding applications vary from very soft elastomers to semirigid elastomers. However, many molding applications require that the molding compositions be rigid at least to the extent that molded parts therefrom are able to maintain their structural integrity and resist deformation upon low energy impact.
It is suggested in the foregoing references that the modulus of elasticity of copolyetheresters may be increased by incorporating therein various reinforcing fillers such as glass and mica. More recently, it has been alleged that the flexural modulus as well as other physical properties may be enhanced by blending with copolyetheresters one or more thermoplastic polyesters. For example, Brown et al (U.S. Pat. No. 3,907,926) have prepared copolyetherester compositions having alleged improved Young's modulus combined with good flexibility and low temperature impact strength by creating a uniform blend of poly(butylene terephthalate) and a copolyetherester. Additionally, Perry et al (UK No. 1,431,916) have prepared blends of a polyester, particularly poly(alkylene terephthalates), and a copolyetherester allegedly having improved impact strength, stiffness and processability. Finally, Charles et al (U.S. Pat. No. 4.469,851) have prepared blends of poly(butylene terephthalate) and a copolyetherester derived from butanediol, butenediol, dimethylterephthalate and poly(tetramethylene ether) glycol which allegedly have improved melt stability.
While the foregoing blends have improved stiffness as manifested by higher flexural modulus, they tend to be too brittle. Specifically, depending upon the amount of polyester in the blend, these compositions are unable to absorb high energy impact without breaking. As the amount of polyester in the blend is increased, the amount of energy the part is able to withstand before break decreases. Unmodified copolyetheresters, on the other hand, are able to withstand said impact without break and are able to withstand even higher energy impact before break finally occurs. However, while the total energy these compositions can withstand before break is high, because of their low flexural modulus, the amount of energy they can absorb before permanent deformation occurs is relatively low.
It is an object of the present invention to provide thermoplastic elastomeric molding compositions which are suitable for a broad range of end use applications having sufficient flexural modulus so as to provide molded parts with good physical integrity and stiffness.
It is also an object of the present invention to provide thermoplastic elastomeric molding compositions which are able to withstand high temperatures with little or no heat sag.
Finally, it is an object of the present invention to provide thermoplastic elastomeric molding compositions which are able to withstand high energy impact before break and/or permanent deformation.
It has now been found that thermoplastic elastomeric molding compositions may be prepared which overcome the foregoing deficiencies and have good overall physical characteristics including high stress-strain properties, good impact resistance and good moldability.